The purpose of this study is to investigate whether mutations in genes coding for Na/Pi-cotransporters are associated with aortic valve calcification. A patient population with premature aortic valve calcification treated with aortic valve replacement will be screened for mutations in these specific genes. Furthermore, aortic valve tissue received from the operations, will be examined for the presence of Na/Pi-cotransporters, and for molecular characterization of the transporters.